You may want to consider...

why your choices are what they are in the search for an answer to your own question. Really! Why do you buy NGC and grade PCGS? Sounds to me that you like the cheaper price of NGC but favor PCGS graded coins for some reason. You'll have to search your own feelings for that answer.

I personally find NGC and PCGS coins equally attractive on a grade-for-grade basis. I do like the cheaper prices of NGC and prefer the NGC slab over that of PCGS. I value each coin equally but understand that the market brings a higher premium for PCGS slabbed coins. My opinion? If you're in it for collecting go for NGC. If you're in it for the money, you probably want to go PCGS. One thing to consider, especially if it is the collecting you enjoy, buy the coin, not the slab.